The present disclosure relates to magnetic materials, and in particular to soft and hard magnetic materials. Soft magnetic materials may be useful as core materials of inductive components.
Inductive components used in electronic devices often require magnetic materials, which desirably exhibit high saturation magnetization, high initial permeability, high resistivity, low magnetic power loss, low eddy current loss, low dielectric power loss, high Curie temperature, variable temperature stability of magnetic and electrical properties, and good mechanical strength.
To date, high frequency magnetic components have employed ferrites as core materials. However, ferrites are limited in part by low permeabilities when compared to metallic materials, poor performance at frequencies greater than 100 MHz, low Curie temperatures, and complex manufacturing procedures. Currently, there is no method available for producing commercial-scale amounts of soft magnetic materials with properties superior to ferrites in the high frequency range (greater than 100 MHz).
Current methods for processing conventional micrometer-sized soft magnetic materials are designed to reduce the total core loss by reducing eddy current loss. Three types of soft magnetic materials are commonly used: metallic ribbons, powdered metals, and powdered ferrites. Metallic ribbon materials comprise Fe—Ni, Fe—Co, and Fe—Si alloys, manufactured in the form of stripes or ribbons using a metallurgy approach, and are used in the frequency range of 10 to 100 kHz. Powdered metal materials are composites consisting of a metallic magnetic phase (Fe, Co, or their various alloys) and a non-magnetic insulating phase. This type of material is made by powder metallurgy techniques and is used in the frequency range of 50 kHz to 500 kHz. Ferrites include materials such as spinel ferrites (e.g., (Ni, Zn)Fe2O4), hexagonal ferrites (e.g., Me2Z, wherein Z=Ba3Me2Fe24O, and Me denotes a transition metal element), and garnet ferrites (e.g., Y3Fe5O12). Ferrites are made by ceramic techniques, and are used in the frequency range from 100 kHz to 100 GHz.
There are a number of disadvantages associated with currently available soft magnetic materials. In conventional micrometer-sized soft magnetic materials, each particle or grain contains many magnetic domains (“multidomain”), which cause interference or resonance. Domain wall resonance restricts the frequency characteristics of the initial permeability. When the size of the magnetic particle is smaller than the critical size for multidomain formation, the particle is in a single domain state. With single magnetic domain particles, domain wall resonance is eliminated, and the material can function at higher frequencies.
None of the three types of magnetic materials meet all of the above-mentioned requirements in soft magnetic applications owing to their associated large core loss. Metallic ribbon materials have excellent fundamental magnetic properties such as high saturation magnetization, high initial permeability, and high Curie temperature. However, a low resistivity (10−6 Ohm-cm) renders them difficult to use at frequencies above 1 MHz. In addition, the mechanical strength of the ribbons is very poor. Powder metals have higher resistivities and, consequently, can be used at higher frequency ranges, but their permeabilities are low. Ferrites are the only practical choice when the working frequency for a device is above 1 MHz, but the magnetic properties of ferrites in the high frequency range are poor. Although extensive efforts have been directed toward improving the performance of these materials, very limited progress has been made.
To date, there appears to be no prior art relating to the use of nanostructured materials in bulk soft magnetic applications. As used herein, nanostructured materials have grains or particles with average dimensions of 1 nanometer to 100 nanometers (nm). A feature of nanostructured materials is the high fraction of atoms (up to 50%) that reside at grain or particle boundaries. Such materials have substantially different, often superior, chemical and physical properties compared to conventional micrometer-sized counterparts of the same composition.
A variety of methods have been developed to produce nanostructured materials, for example production by condensation from the vapor phase. This inert gas condensation methodology has been developed by Nanophase Technologies to produce TiO2 and Al2O3 in commercial-scale quantities. Another technique for making nanostructured metal and ceramic powders is by mechanical milling at ambient or at liquid nitrogen (cryomilling) temperature. A third approach is chemical synthesis from inorganic or organic precursors, which has been used to produce nanostructured WC/C.
Recently, nanostructured FeMOx (wherein M is Hf, Zr, Si, Al or a rare-earth metal element) thin films have been obtained by Hadjipanayis et al and Hayakawa et al, via atomic deposition. These are nanostructured composite thin films deposited on substrates, where the thin film is composed of nanostructured magnetic particles surrounded by an amorphous insulating phase. However, the atomic deposition approach is limited to thin film applications, and is not suitable for bulk materials or thick films.
Fe/silica nanostructured composites have been proposed for use in magnetic refrigeration applications. The nanostructured composites are a mixture of iron particles with silica ceramic, but such composites are limited to magnetic refrigeration, and cannot be used for high frequency magnetic applications. Preparation of magnetic nanostructured composites using a wet chemical synthesis technique has been described for a Fen/BN composite by the ammonolysis of an aqueous mixture solution of FeCl3, urea, and boric acid, followed by thermochemical conversion to the final product. While the synthesis of other magnetic nanostructured composite systems have been described, none of these materials is suitable for high frequency soft magnetic applications requiring reduced core loss. There accordingly remains a need for compositions and methods for large-scale manufacture of soft magnetic materials, especially bulk materials useful above about 1 MHz.